in my post there is a link for a powerful source of these waves but any source is good enough.
How would rogue gravitational waves create matter?
Here I use an analogy with the waves in the ocean that were discovered to create very strong unexpected phenomenas. When a field is strong enough it can create matter. So, it would be something similar to Hawking radiation or creation of electron positron pairs from gamma rays.
What do you mean by “net zero energy”?
I was most impressed by a single fact of physics that all energy in ordinary matter is equal to the negative potential gravitational energy of that matter.
How would this [creation of matter and gravitational fields] increase the expansion of the universe?
I read somewhere, maybe quantum gravity theories, where one creates the other, so I would have to search it again, unless someone here can help me.
(…) black body CMB?
Please notice that inside another comment in this post I have addressed that question.